Fluid & Electrolytes Overview

Fluid & Electrolytes Overview

• Insensible Loss: Refers to fluid loss through perspiration and sweat, not easily measured.

Body Fluid Composition

• ICF (Intracellular Fluid): Comprises 2/3 of body fluid, found within cells; major site of potassium (K+).
• ECF (Extracellular Fluid): Accounts for 1/3 of body fluid, located outside of cells; includes interstitial, intravascular, and transcellular compartments.

ECF Components

• Interstitial Fluid: Fluid between cells and outside blood vessels, contains lymph.
• Intravascular Compartment: Blood plasma within the veins, essential for circulatory function.
• Transcellular Compartment: Encloses fluids like cerebrospinal fluid (CSF), sweat, and synovial fluid.

Factors Influencing Body Water

• Adipose Tissue Impact: Higher fat content leads to lower water volume as fat takes up space.
• Water-Rich Areas: Muscle, skin, and blood are primary areas containing substantial amounts of water.

Fluid Balance Indicators

• Urine Output: The primary indicator for assessing fluid balance and proper fluid shifting.

Osmosis and Related Concepts

• Osmosis: Fluid movement from lesser to greater solute concentration, aiming for equilibrium.
• Osmotic Pressure: The force that draws water towards high solute concentration; relevant in conditions like increased intracranial pressure.
• Osmolarity: Measures the concentration of solutes relative to water in a solution.

Solution Types and Effects

• Hypertonic Solutions: Contain more solutes, causing cells to shrink as fluid moves from ICF to ECF for hydration. Examples include D10W and D5W in 0.9% NS.
• Isotonic Solutions: Maintain fluid shift without changing cell size; expand ECF. Examples are Lactated Ringer's and NS 0.9%.
• Hypotonic Solutions: Shift fluid into cells when ECF solute concentration is too low. An example is 0.45% NS.

Other Key Concepts

• Colloids: Used to shift fluid back to intravascular space, effective in treating third-spacing.
• Leaky Membranes: Indicates pathology where proteins and fluid escape to interstitial space, leading to complications with diuretics.

Diffusion and Filtration

• Diffusion: Movement of solutes from high to low concentration across a semi-permeable membrane, such as oxygen and carbon dioxide exchange in the lungs.
• Filtration: Process of moving water and solutes from higher to lower pressure regions.

Electrolyte Management

• Primary Electrolytes: K+ is predominant in ICF; Na+ and Cl- dominate ECF.
• Measurement: Electrolyte levels are measured in mEq, while calcium (Ca++) and phosphate (PO4-) are in mg/dL.

Renal Function and Fluid Balance Indicators

• GFR (Glomerular Filtration Rate): Normal value should be greater than 60, indicates kidney filtering capacity.
• Creatinine & BUN Levels: High levels indicate kidney dysfunction (creatinine) or dehydration (BUN), with normal ranges being 0.5-1.5 for creatinine and 10-20 for BUN.

Caution with IV Solutions

• Risk of Overload: Hypertonic IV solutions can lead to volume overload if not monitored carefully, necessitating vigilance in patient management.

IV Solution Classifications

• D5W: Isotonic
• D10W, NS 3%-5%: Hypertonic
• 0.45% NS (1/2 NS): Hypotonic
• Lactated Ringer's: Isotonic

Understanding fluid and electrolyte dynamics is crucial for effective patient care and managing various conditions related to hydration and electrolyte imbalances.